Printing plate composition



Patented Oct. 29, 1940 UNITED STATES PATENT OFFICE No Drawings.

Application July 31, 1939, erial No. 287,559

1'! Claims. (01. 41-25) This application is a continuation in part of mypreviously filed application, Serial No. 64,163, filed February 15,1936.

My invention relates to printing plates, and

5 has for its object to provide a device of this character which shallbe extremely durable, economical of manufacture, and simple in itsadaptation or use, and which may be employed in any type of printingwork, and particularly in lieu of electrotype or stereotype plates,metal embossing panels, and similar plates used by printers andembossers.

A further object of my invention is to provide a plastic composition,which, under the influence of heat and pressure, may be molded toreproduce in detail any printing setup upon which it is impressed, andform a printing plate with an extremely hard, durable surface havingsuperior ink distributing properties.

As is well known in the art to which my invention relates, printingplates, such as electrotypes and embossing plates, are expensive,require considerable skilled labor to produce, and the process ofpreparing them consumes from 2 three hours to several hours. The metalemployed for the printing surfaces, such as copper or nickel, beingmalleable, the plates break down or flow under use, and are liable to beruined by being dropped or by being accidentally struck 30 with a hardobject so as to deface the printing surface.

By the use of my improved composition, a plate may be produced in a fewminutes which, in detail of reproduction, is superior to theelectro- 35type, which has superior ink distributing qualities, and which has anexceedingly hard tough surface, which is not liable to damage by use, byrough handling, or by being accidentally struck.

Printing plates made from plastic composi- 40 tions have heretofore beenproposed in the art,

but the use of such plates has been greatly limited due to the fact thatthe substances heretofore proposed are liable to shrinkage and towarping, would become brittle and break down 45 in service or else flowand become distorted when printing, and are not readily wettable by oilyprinting inks, such as are employed with metallic plates. Also, withsome substances heretofore proposed, the printing inks having an'oilbase 60 have a plasticizing or solvent effect on the composition causingit in flow in service. (Electro- -typers Bulletin, May, 1937; pages29-36.)

I have discovered that a plastic binding material moldable under heatand pressure, having 65 incorporated therein in suitable proportions, as

hereinafter. set forth, a plasticizer and a metal compound having theproperty of providing the requisite hardness and strength and a surfacesuitable for holding and distributing ink, may be formed into a sheetwhich is admirably 5 adapted for the production of printing plates. Whena sheet so formed is subjected to pressure under the influence of heat,it produces a surface of extreme hardness and durability. The metalcompound in combination with the plasticizer in 10 proper proportionsaffords the requisite hardness for the surface of the plate, and has theproperty of being wetted by oily ink, making it capable of holding theprinting ink without smearing and yet retain the necessary sharpness ofoutline reql5 uisite to reproduce faithfully minute details of a design.This also permits the use of a thinner ink than may be used with otherplates, including metal plates, and my improved plate is thus capable ofmore satisfactory detail reproduction. 20

The plastic binding-material chosen is preferably one that is readilysoluble in a volatile solvent, such as acetone or alcohol, and one whichmay be molded under the influence of heat and pressure. I have foundthat a fire resistant plastic cellulosic compound, such as celluloseacetate with suitable plasticizers in the right proportions, isadmirably suited for my improved product. While pyroxyiin may be mixedwith plasticizers and mineral filler, as hereinafter described, andmolded to form a printing plate, it is not so satisfactory as celluloseacetate, and I have found that its inflammability renders the necessarymachining operations hazardous.

The use of plasticizers to counteract the tendency of cellulosic estersto become brittle with age is well known. I have found that theselection of plasticizers compatible with each other and with celluloseacetate, the mineral compound incorporated in the mixture, and theproportions 40 employed, are highly important considerations inproducing a printing plate having sufficient hardness, toughness anddurability to stand up under the severe service conditions to which sucha plate is ordinarily subjected.

The mixture of plasticizers which I employ imparts to the plasticmixture a hardness and strength together with a softening pointsufliciently high for the material not to flow at temperatures andpressures encountered in service. The plasticizers must have as high aboiling point as possible in order to avoid loss in'the moldingoperation. They must also have low vapor pressures at ordinarytemperatures so that they will not have a high evaporation rate and thuslose 56 tioizers should impart fire resistance to the material so thatit may be safely molded at relatively high temperatures .and subjectedto machining operations.

I have found that a mixture of the following plasticizers with celluloseacetate and a suitable metal compound produces a material having idealcharacteristics for forming a printing plate:

Percent by volume of Boilin iinishedprodpoint,

not

1 Methyl hthslyl ethyl 'glycollate mm.

(santicl er M17) 3. 24-4. 86 189/5 2 Butyl phthalyl butyl glycollate(Santiclzer B16) (MN-10.51 210/6 3 Triphenyl phosphate 9. 63-1447 245/11It will be noted that the boiling points of all of the aboveplasticizers are very high compared to the molding temperatures ofcellulose acetate. Also the vapor pressures at atmospheric temperaturesare very low. The composition thus formed does not lose plasticizereither in molding or in storage. The first two plasticizers producemoldability suitable for a printing plate and impart toughness to theplate. Triphenyl phosphate provides hardness and strength. It will benoted that the latter, in weight, comprises substantially the sum of theweights of the other two plasticizers.

In place of the Santicizer M17, I may substitute ethyl phthalylglycollate. In place of the Santicizer B16 I may use a mixture of orthoand para.

toluene ethyl sulfonamides, a mixture of ortho and para toluenesulfonamides, ortho-cresyl paratoluene sulfonate, or other similarsulfonamide condensation products compatible with cellulose acetate andwith the other plasticizers employed. In lieu of triphenyl phosphate,tri-butyl phosphate may be substituted. It will be understood, however,that where substitutions are employed the proportions hereinafter givenwould necessarily have to be varied in order to produce the requiredsoftening point and molding temperature. It will also be apparent thatany plasticizers chosen must be compatible with cellulose acetate andwith each other in the proportions employed.

For the best results, I have found that the mixture of cellulose acetateand plasticizers should have a softening point in the neighborhood of275 F. to 295 F., and a molding temperature around 350 F. If thesoftening point is above 295 F., it is too brittle or has too low atensile strength for use in a printing plate. If the sofcarbonate,kaolin,

as the best bases for oil paints, notably basic lead carbonate and ironoxide, are the metal compounds best suited for making my improvedprinting plate. The qualities of these compounds are such that thestrength, hardness and durability of the plastic in which they areincorporated are enhanced. When incorporated in the proportionshereinafter specified, the particles appear on the surface of the plateand have the quality of being readily wetted by and of retainingordinary printing ink, particularly that having an 011 I have alsoproduced moldable plates with other compounds and metals, such as zincoxide, calcium carbonate, calcium sulphate, manganese barium sulphate,magnesium oxide, magnesium carbonate, alum, metallic aluminum, tinoxide, and manganese oxide, but find such plates less durable, in thatthey are more brittle, or are else subject to cold flow in service, andhave less ink retaining and distributing properties than those producedwith lead carbonate and iron oxide.

I have found that the lead carbonate and iron oxide have qualities forthis purpose superior to those mentioned in the last group, or to thepure metals in powdered form. While I have had no means at hand foraccurately determining the relative wetting properties of the metalcompounds in relation to the cellulose binding material, it is myobservation that the metal compounds which are the more difiicultlywetted in a solution of cellulose acetate produce the tougher and harderplates.

For all round purposes, a printing plate made from my improved mixtureusing lead carbonate or iron oxide, or a mixture of the two, ispreferable. The surface thus produced appears to be the best adapted forholding most printing inks. Also the plate is tougher, harder, and moredur- 'able than those made with other metallic comlustration, of apreferred composition forming my improved printing plate:

Parts by Percent by Parts by Percent by weight weight volume volumeCellulose acetate.. 70 35. 0-25. 0 53. 0 56. 0-49. 0 Plasticizers:

Santicizer M17. 5 2. 5- 1. 75 4. 2 4. 4-3. 9 Banticizer B16- 10 5. 0-3.5 9. l 9. 5-8. 4 Triphenyl phosphate 15 7. 5-4. 75 12. 5 13. 1-11. 4Lead carbonate -185 50. 065.0 16.0-30.0 17.0-28.0

3 Where iron oxide or, a mixture of lead carbonate and iron oxide isemployed as the metal compound, the weight ratios will vary according tothe specific gravities and the bulking values of the compounds.Generally speaking the volume ratios will be substantially the same forall compounds employed.

I havefound that the proportions of the metal compound employed asherein set forth are very important. If less than 16.0% by volume byweight of lead carbonate) be employed, the resulting plate will belikely to cold flow in service. On the other hand, if more than 30.0% byvolume of metal compound (65% by weight of lead carbonate) be employed,the plate will be too brittle and the characters are likely to breakdown.

In the practical carrying out of my invention, I first place in asuitable mixing vessel one equivalent weight of acetone or othersuitable solvent for each unit weight of the finished product. Celluloseacetate is then added to the solvent slowly, the mechanical mixer beingrun until it is thoroughly dissolved in the solvent without lumping. Theplasticizers are then added to the solution of cellulose acetate in thesolvent and the mixing continued until the plasticizers are thoroughlyincorporated. Depending on the type of mixer employed, this shouldrequire only a short period of time. As soon as the plasticizers arethoroughly incorporated into the mix, the metal compound is then addedslowly and mixing continued. Inasmuch as the compounds are difficultlywettable in the mixture, they are difflcult .to disperse and, dependingupon the type of mixer, may require from 24 to 48 hours for thoroughdispersion in the batch. As soon as the metal compound is thoroughlydispersed, the mixture is extruded into thin sheets of from .005 to .007inch in thickness and allowed to dry. If air ata temperature of 90 to100 C. be passed over the sheets, they may be dried in a few minutes. Ifthicker sheets are made, the solvent may be locked in by surface dryingand a considerable aging time may be necessary to rid the mixture of thesolvent.

After the sheets have become thoroughly dry, they are placed in layersor laminations in a suitable press, heated to molding temperature,

'which is in the neighborhood of 350 F., and

pressed into a sheet of suitable thickness for forming a printing plate.For practical purposes, this should be about one-eighth of an inch inthickness.

In forming the plate, a suitable matrix is first formed in any mannerknown to those skilled in the art, of a sufficiently hard substance towithstand pressure and capable of withstanding heat. Suitable matricesmay be made of plaster of Paris, phenolic plastic compositions,impression metal or other substance of corresponding hardness. Thismatrix is placed in a press, such as a copying press, hydraulic press,or other suitable press, having heating and cooling means associatedtherewith. One or both of the platens of the press are then heated to atemperature of from 330 F. to 360 F'., and over the matrix is placed asheet of my improved composition prepared as hereinbefore described. Thesheet is pressed into the matrix and the plate is formed. The press isthen cooled and the plate stripped from the matrix. It is next trimmed,routed and mounted on a suitable backing. If the plate is to be used ina rotary press it may be heated and curved over a suitable form to fitthe cylinder on which it is to be mounted.

I have found that printing plates made of the compositions, and inaccordance with myimproved process, are extremely durable, and are notliable to damage by being accidentally struck or dropped. For example,in the operation of a printing press with one of my improved plates, thepaper strippers of the press accidentally struck the plate a number oftimes without damaging in any way the printing surface of the plate.While the filler does not appear to enter into chemical combination withthe binding material, it imparts to it a hardness and toughness farbeyond that possessed by the binding material alone. Further, thecompositions herein described may be machined more readily than cancellulose acetate alone, rendering them adaptable for uses otherthanprinting plates.

I have found also that my improved printing plates are particularlyadapted for reproducing details of impressions, such as fine lines andfine screen photo etchings, or any other'details known to the printingart.

, While I have described my inventionin several forms, it will beobvious to those skilled in the art that it is not so limited, but issusceptible of various other changes and modifications, withoutdeparting from the spirit thereof, and I desire, therefore, that onlysuchlimitations shall be placed thereupon as are imposed bythe prior artor as are specifically set forth in the appended claims.

What I claim is:

1. A composition for making relief printing plates and the likecomprising a sheet of material deformable under heat and pressure andcomposed of a metal compound approximating one-fourth of the volumethereof and selected from lead carbonate and iron oxide, a cellulosicplastic approximating 49% to 56% by volume, and a non-volatileplasticizer of from 17% to 28% by volume.

2. A composition for making printing plates and the like comprising ametal compound in an amount equivalent to approximately onefourth thevolume thereof selected from lead carbonate and iron oxide, celluloseacetate in an amount equivalent to 49% to 56% of the volume thereof, andthe remainder a non-volatile plasticizer to give the mixture a softeningpoint of approximately 290 F. and a molding temperature' ofapproximately 350 F.

3. A composition for making printing plates and the like comprising asolid mineral compound comprised of a mixture of lead carbonate and ironoxide in an amount equivalent to approximately one-fourth the volumethereof, cellulose acetate in an amount equivalent to 49% to 56% of thevolume thereof, and the remainder a non-volatile plasticizer to give themixture a softening point of approximately 290 F. and a moldingtemperature of approximately 350 F., the plasticizer comprising amixture of organic glycollates and an organic phosphate compatible withcellulose acetate and with each other.

4. A composition for making printing plates and the like comprising asheet of material composed of carbonate of lead 17.0% to 28% by volumein suspension in cellulose acetate, and a plasticizer having a boilingpoint considerably above 350 F. and a low vapor pressure whereby it isnon-volatile at atmospheric temperatures.

5. A composition for making printing plates and the like comprisingcellulose acetate 49% to 56% by volume, iron oxide approximatelyonefourth by volume, and the remainder a mixture of placticizers givingto the finished product a softening point in the neighborhood of 290 F.and a molding temperature in the neighborhood of 350 F., saidplasticizers having boiling points considerably above the moldingtemperatures of the composition and being non-volatile at atmospherlctemperatures.

6. A composition for making printing plates and the like comprisingcellulose acetate 49% to 56% by volume, a metal compound selected fromlead carbonate and iron oxide approximately one-fourth by volume, andthe remainder a mixture of plasticizers giving to the finished product asoftening point in the neighborhood of 290 F. and a molding temperaturein the neighborhood of 350 F., said plasticizers having boiling pointsconsiderably above the molding temperatures of the composition and beingnonvolatile at atmospheric temperatures.

7. A composition for making printing platesand the like comprisingcellulose acetate 49% to 56% by volume, lead carbonate approximatelyone-fourth by volume, and the'remainder a mixture of plasticizers givingto the finished product a softening point in the neighborhood of 290 F.and a molding temperature in the neighborhood of 350 F'., saidplasticizers having boiling points considerably above the moldingtemperatures of the composition and being nonvolatile at atmospherictemperatures.

8. A composition for making printing'plates and the like comprisingcellulose acetate 49% to 56% by volume, a metal compound comprising leadcarbonate and iron oxide diflicultly wettable in the cellulose acetateand readily wettable by oily printing ink and constituting approximatelyone-fourth by volume, and the remainder a mixture of plasticizers givingto the finished product a softening point inthe neighborhood of 290 F.and a molding temperature in the neighborhood of 350 F., saidplasticizers having boiling points considerably above the moldingtemperatures of the composition and being non-volatile at atmospherictemperatures 9. A composition for making printing plates and the likecomprising cellulose acetate 49% to 56% by volume, a metal compoundcomprising lead carbonate and iron oxide 17% to 28% by volumedifilcultly wettable in the cellulose acetate and readily wettable byprinting ink, and the remainder a mixture of plasticizers giving to thefinished product a softening point in the neighborhood of 290 F. and amolding temperature in the neighborhood of 350 F., said plasticizershaving boiling points considerably above the molding temperatures of thecomposition and being non-volatile at ordinary temperatures.

10. A printing plate composed of a solid metal compound selected fromlead carbonate and iron oxide in finely divided form equivalent to to28% by volume thereof, cellulose acetate in an amount equivalent to 49%to 56% by volume thereof, and the remainder a mixture of plasticizerswhich give to the plate a softening point considerably above 200 F.

11. A printing plate composed of a metal compound comprising leadcarbonate and iron oxide in finely divided form equivalent to 17% to 28%by volume thereof, cellulose acetate in an amount equivalent to 49% to56% by volume thereof, and the remainder a mixture of plasticizerscomprising a mixture of methyl collate, butyl phthalyl phenyl phosphate.

12. A printing plate composed of a metal compound selected from leadcarbonate and iron oxide in finely divided form equivalent to 17 to 28%by volume thereof, cellulose acetate in an amount equivalent to-4 to byvolume thereof, and the remainder a mixture of plasticizers comprising amixture of methyl phthalyl ethyl glycollate, butyl phthalyl butylglycollate, and triphenyl phosphate the triphenyl phosphate comprisingapproximately as much by weight as the sum of the weights of the othertwo plasticizers.

13. A relief phthalyl ethylglybutyl zlycollate, and triprinting platecomposed of carbonate of lead in an amount equivalent to 18% to 28% ofthe volume thereof, a plastic fire resistant cellulosic binder amountingto 48% to 6% of the volume thereof, and the remainder a mixture ofplasticizers compatible with cellulose acetate and with each othergiving to the gionting plate a molding point of approximately 14. Aprinting plate composed of carbonate of lead in an amount equivalent to7% to of the volume thereof, cellulose acetate amounting to 49% to 56%of the volume thereof, and the remainder a mixture of plasticizerscompatible with cellulose acetate and with each other giving to theprinting plate a molding temperature of approximately 350 F.

I 1a. A printing plate comprising a sheet com--. posed of a metalcompound selected from lead carbonate, and iron oxide in finely dividedform in an amount equivalent to 17% to 28% of the volume thereof, athermoplastic fire resistant cellulosic binder for said metalliccompound through which it protrudes to be wetted by the ink andamounting to 49% to 56 of the volume of the plate, and the remainder amixture of plasticizers compatible with cellulose acetate, non-volatileat atmospheric temperatures, and giving to the composition a moldingtemperature of approximately 350 F.

16. A relief printing plate in the form of a sheet comprising by volume17% to 28% of one or more mineral compounds in finely divided form whichare readily wettable by printing ink and which are selected from thefollowing: lead carbonate and iron oxide; and 49% to 56% of athermoplastic fire resistant cellulosic binder in which the selectedcompound or compounds are so dimcultly wettable that they are exposed atthe surface of the binding material to be wetted by the ink in theprinting operation, and the remainder a mixture of plasticizerscompatible with the cellulosic binding material non-volatile atatmospheric temperature and giving to the plate a molding temperaturearound 350 F.

17. A composition for making printing plates and the like comprising asheet of material composed of a metal compound of the group consistingof carbonate of lead and iron oxide amounting to 17% to 28% by volume ofthe composition in suspension in a cellulosic plastic, and a plasticizerhaving a boiling point considerably above 350 F. and a low vaporpressure whereby it is non-volatile at atmospheric temperatures.CLARENCE E. BOUTWELL.

